1. Field of the Invention
The present invention pertains to telecommunications, and particularly to paging of a mobile station within a cellular telecommunications system.
2. Related Art and other Considerations
In recent years cellular telephones have become increasingly popular. A cellular telephone is just one example of what is referred to in telephone parlance as a "mobile station" or "mobile terminal". Telecommunications services are provided between a cellular telecommunications network and a mobile station (e.g., cellular telephone) over an air interface, e.g., over radio frequencies. At any moment an active mobile station is communicating over the air interface with one or more base stations. The base stations are, in turn, managed by base station controllers (BSCs), which in some systems are also known as radio network controllers (RNCs). The radio network controllers are connected via control nodes to a core telecommunications network. Examples of control nodes include a mobile switching center (MSC) node for connecting to connection-oriented, circuit switched networks such as PSTN and/or ISDN, and a general packet radio service (e.g., GPRS) node for connecting to packet-switched networks such as Internet, for example.
The radio transmissions of each base station cover a particular geographical area. As used herein, the geographical area into which radio transmissions of a base station extend is termed a "cell". Such definition of "cell" thus encompasses systems in which the perspective is such that a base station covers a single cell, as well as systems wherein the term "cell" is differently employed in a manner such that a base station serves more than one cell. Regardless of perspective, a handoff or handover must occur as a mobile station travels from an old cell to a new cell (e.g., for example when the mobile travels into a cell covered by different base stations and or different RNCs). This permits mobile stations to "roam" considerable distances.
In view of the extent to which a mobile station can travel, location management of a mobile telecommunications system can be extensive. A number of geographical area levels can be utilized. In this regard, cells can be grouped into larger areas, for example into location areas. A location area can be served by plural radio network controllers (RNCs). Location areas are discussed, for example, in U.S. patent application Ser. No. 08/916,285, filed Aug. 22, 1997, entitled "GEOGRAPHICAL RESTRICTION IN CELLULAR TELECOMMUNICATIONS NETWORK", which is incorporated herein by reference. In view e.g., of the potential complexity of such location management schemes, an effort is made to keep track of the location of the mobile station while trying to minimize the radio resources devoted to such effort.
One method for saving radio resources involves location updating messaging. In location updating, when a mobile station which is idle (i.e., there is no current connection between the mobile station and the network) moves into a cell belonging to a new location area, the mobile station apprises of its whereabouts by sending a message known as a location update. The location update message must be sent so that both a home location register (HLR) maintained for the mobile station and a visitor location register (VLR) have appropriate current information about the mobile station and its whereabouts. Then, when the network needs to establish a connection or exchange data with the mobile station, the mobile station is paged within the last location area apprised by the mobile station. The mobile station answers the page by sending a page response message to the network from the cell where the mobile station is currently located.
As indicated above, the aforementioned location updating is utilized when the mobile station is idle (e.g., is not participating in an ongoing call). Moreover, when the mobile station is idle the location updating is applicable not only to circuit switched services (which can involve speech services and/or data services), but also to packet switched services as well. Whereas in circuit switched services the data user has radio resources continuously reserved for the connection to the radio network during a data call (e.g., even when not transferring data), in packet switched services the user has radio resources reserved for the connection to the radio network only when either (1) the mobile station desires to transmit or (2) the network has something to transmit to the mobile station. In other words, in the packet switched service the mobile station (e.g., a computer with mobile termination) does not have radio resources reserved for the connection to the network constantly while the computer is in use, but only during these two transmission events. One example of packet switched service recently available within the GSM (Global System for Mobile communications) system is General Packet Radio Service (GPRS).
When a mobile station is connected with the network during a connection involving a packet-switching service, procedures such as cell updating and routing area updating are employed. When the mobile station moves into a new cell, it updates the network with its location on a cell level. However, in periods of no data transfer, cell updating wastes radio resources. Instead routing area updating is used in periods of no data transfer. Thus, the routing area updating typically occurs only during the lifetime of the packet-switched connection. A routing area is a group of cells. The routing area is typically smaller than a location area. Since traffic for a packet switched service is very bursty in nature with long periods of no packet transfer, it would be a waste of radio resources to have a radio channel continuously assigned to a connection. Instead, when the mobile station moves into a new routing area, the mobile station updates the network with its current location, e.g., with its current routing area, similar to the location area update described above. When a packet is to be sent from the network to the mobile station, and when the location of the mobile station is known only at the routing area level, a paging message is sent in all cells belonging to the routing area where the mobile made its last routing area update.
Location areas and routing areas, although generally having differing purposes, are hereinafter referred to as multicell areas. A cell can be included in more than one multicell area. Two or more multicell areas that contain such a cell are said to be "overlapping". The use of overlapping multicell areas can limit the "ping-pong" effect at borders between exchanges (e.g., as between mobile switching centers (MSCs). The ping-pong effect occurs when a mobile station repeatedly crosses between two cells which belong to different multicell areas. When the ping-pong effect is present, the mobile station must update its multicell area with each such crossing. Moreover, ping-pong effects generate much undesirable additional signaling within the network, e.g., between MSCs.
In current cellular telecommunications systems, distribution of paging is handled in a truly hierarchial manner. In this regard, an MSC distributes a page to all RNCs that control cells within the area where the mobile station is to be paged (e.g., a location area or a routing area). The RNCs then send each page request to all base stations transmitting and receiving radio signals which (1) are controlled by the RNC; and (2) are located within the area where the mobile station is to be paged (e.g., a location area or a routing area). The base stations then send the actual paging signal over the air interface.
Certain paging procedures are accommodated within the GSM (Global System for Mobile communications). For example, GSM 09.02 Version 5.8.0, February 1998, GSM MAP specification, Chapters 6.2.1-6.2.2, Paging and Search, cater to the possibility for a VLR to request paging from an MSC. As ascertained from this specification, the VLR knows the location area where the mobile station is supposedly located, and forms paging signals which are to be sent to the BSCs. However, the MSC and the VLR have a one-to-one relationship; i.e., there is one VLR for each MSC. The MSC and VLR are also two differing node types, representing differing functionality types.
GSM also allows for a Serving GPRS Support Node (SGSN) to receive a paging request from the MSCNVLR. An SGSN is a type of MSC handling only packet switched services, and has a different functionality than the MSC/VLR. In the SGSN, the routing area where the mobile station is located is stored in case the mobile station is attached to the GPRS service (mentioned above). See GSM 03.60, GPRS Service Description, Chapter 6.3, Interactions Between SGSN and MSCNVLR.
In the Pacific Digital Cellular standard for inter-MSC paging, appearing in document TTC JJ-70.10, chapter 3.3.1.2 (1995), paging distribution is accomplished by an anchor mobile switching center (AMSC) from which the terminating call was routed to other MSCs. Thus, this standard involves the core network in paging distribution (being at the MSC level), and requires that the core network have knowledge of the cell topology.
It may, in some instances, be desirable to have a telecommunications network with a strict functional division between a "core network" (to which the MSC belongs) and the radio access network (which includes the RNCs). According to this strict functional division, the radio access network would handle all radio related operations (for example, the knowledge of which base stations, cells, and channels are to be used to obtain radio coverage and capacity within a certain geographical area). In other words, the core network (specifically including the MSC) would not have knowledge regarding cell structure, and more specifically would not know what particular cells form a given location area.
In a cellular network having the strict functional division described above, a problem would occur when the core network needs to page a mobile station that is idle. The page should be sent to all cells within the location area. However, the core network (e.g., the MSC) does not know to which RNCs the page should be sent.
A similar problem can exist for a mobile station having a packet switched connection. There is no continuously reserved radio resource for the packet switched connection. Instead, the connection is maintained by using routing area updating. That is, the mobile station sends a routing area update message to the network when the mobile station comes into a new routing area. The identity of the routing area where the mobile station is currently located is stored in the RNC which controls the connection to the mobile station, known as the Serving RNC or SRNC. For limiting the above-described ping-pong effect, the mobile station's routing area may also include cells that are controlled by RNCs other than the RNC which is currently in control of the packet switched connection to the mobile station (i.e., other than the SRNC). The problem arises when the MSC is to send a packet to the mobile station, and therefore a need to page the mobile station from the base stations for each cell belonging to the routing area. In other words, somehow a page needs to be sent by RNCs other than the Serving RNC. Yet, with strict functional division, the MSC has no knowledge of the plan of the radio access network and thus no knowledge of which RNCs should be involved in paging the mobile station.
What is needed therefore, and an object of the present invention, is a technique for paging a mobile station in a multicell area, particularly when the core network does not know from which nodes a paging message should be issued.